1. Technical Field of the Invention
The present invention relates to a lithium secondary battery comprising a cathode including a material that can be doped/undoped with lithium ions as an active material; an anode including a lithium metal, a lithium alloy, or a material that can be doped/undoped with lithium ions as an active material; and a liquid or solid electrolyte, and to the cathode active material for use in the lithium secondary battery.
2. Related Art of the Invention
With a rapid advance of portable and cordless electronic devices, demands for a lithium secondary battery which can realize small size, lightweight and a large capacity compared to the conventional secondary batteries have been increasing.
As a cathode active material in a lithium secondary battery, lithiated cobalt dioxide has been studied and it has already been put into practical use in the lithium secondary batteries as a power source for cellular phones and camcorders. Recently, lithiated nickel dioxide using a nickel compound as a raw material which is cheaper than cobalt compound and abundant in terms of resources has been examined actively.
Lithiated nickel dioxide, as well as lithiated cobalt dioxide, is a compound having an .alpha.-NaFeO.sub.2 structure. However, it is difficult to synthesize lithiated nickel dioxide compared to lithiated cobalt dioxide, because nickel is easily substituted at a lithium site in lithiated nickel dioxide. Recent progress in the synthetic conditions has offered substantial practicability of stoichiometric composition of lithiated nickel dioxide presenting a high discharge capacity. However, the lithiated nickel dioxide still suffers capacity drop-off associated with repeated cycles of charging/discharging processes at high capacity, or in other words, a poor cycle characteristic.